Rare earth element oxyflouride powder spray material and sprayed article

ABSTRACT

A spray material comprising rare earth element oxyfluoride particles having an aspect ratio of up to 2, an average particle size of 10-100 μm, and a bulk density of 0.8-2 g/cm 3 , and containing not more than 0.5 wt % of carbon and 3-15 wt % of oxygen is suitable for air plasma spraying. An article having a sprayed coating of rare earth element oxyfluoride has high resistance against plasma etching and a long lifetime.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2012-183302 filed in Japan on Aug. 22, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a thermal spraying material in the form ofrare earth element oxyfluoride powder, especially suited for use to forma sprayed coating having high corrosion resistance in a corrosive plasmaatmosphere as encountered in the semiconductor device fabricationprocess, and an article having a sprayed coating of the thermal sprayingmaterial.

BACKGROUND ART

In the prior art, sprayed coatings having high corrosion resistance areused for protecting substrates in a variety of service environments.While aluminum, chromium and similar metal oxides are often used as thethermal spray material, the sprayed coatings of these oxide materialsare susceptible to corrosion upon exposure to hot plasma. Thesematerials are thus inadequate for use in the semiconductor manufacturingprocess which may typically involve treatment in a halogen-basedcorrosive gas plasma atmosphere.

The halogen-based corrosive gas plasma atmosphere used in thefabrication of semiconductor devices contains fluorine-based gases suchas SF₆, CF₄, CHF₃, ClF₃ and HF or chlorine-based gases such as Cl₂, BCl₃and HCl.

Known articles which can be used in such extremely corrosive atmospheresinclude, for example, articles having corrosion resistant coatingsformed thereon by spraying yttrium oxide (Patent Document 1) and yttriumfluoride (Patent Documents 2 and 3) to their surface. While rare earthelement oxide sprayed articles are generally prepared by plasma sprayingrare earth element oxide, they are long used as the sprayed articles inthe industrial semiconductor fabrication process because of leasttechnical problems. On the other hand, the rare earth element fluoridesprayed coatings suffer from a technical problem despite good corrosionresistance. The plasma spraying of rare earth element fluoride has theproblem that when the rare earth element fluoride is passed through aflame at 3,000° C. or higher for melting, the fluoride can be decomposedso that the material partially converts to a mixture of rare earthelement fluoride and rare earth element oxide. For this reason,practical utilization of rare earth element fluoride sprayed articles isdelayed as compared with the rare earth element oxide sprayed articles.

CITATION LIST

-   Patent Document 1: JP 4006596 (US 6852433)-   Patent Document 2: JP 3523222 (US 20020015853)-   Patent Document 3: JP-A 2011-514933 (US 20090214825)

DISCLOSURE OF INVENTION

An object of the invention is to provide a thermal spray material in theform of rare earth element oxyfluoride powder which is used to formsprayed coatings having higher corrosion resistance than conventionalsprayed coatings of rare earth element oxide or fluoride, and a sprayedarticle having a sprayed coating of rare earth element oxyfluoride.

The inventors have found that a spray material comprising rare earthelement oxyfluoride particles having an aspect ratio of up to 2 as shapeindex, an average particle size of 10 to 100 μm, and a bulk density of0.8 to 2 g/cm³, and containing not more than 0.5% by weight of carbonand 3 to 15% by weight of oxygen is effective for plasma spraying, andthat better results are obtained by plasma spraying the rare earthelement oxyfluoride spray material onto a substrate such that thesprayed coating may have a carbon content of up to 0.1% by weight and anoxygen content of 3 to 15% by weight.

In one aspect, the invention provides a spray material comprising rareearth element oxyfluoride particles having an aspect ratio of up to 2,an average particle size of 10 to 100 μm, and a bulk density of 0.8 to 2g/cm³, and containing not more than 0.5% by weight of carbon and 3 to15% by weight of oxygen.

Preferably, the rare earth element is one or more elements selected fromthe group consisting of Y and Group 3A elements from La to Lu.Typically, the rare earth element is Y, Gd or Er.

The spray material is preferably obtained by mixing 10 to 70% by weightof rare earth element oxide particles having an average particle size of0.01 to 5 μm and the balance of rare earth element fluoride particleshaving an average particle size of 0.1 to 5 μm, agglomerating, andfiring.

In another aspect, the invention provides a rare earth elementoxyfluoride-sprayed article comprising a substrate and a sprayed coatingwhich is deposited on the substrate by plasma spraying the spraymaterial defined herein, the sprayed coating having a carbon content ofnot more than 0.1% by weight and an oxygen content of 3 to 15% byweight.

ADVANTAGEOUS EFFECTS OF INVENTION

The spray material in the form of rare earth element oxyfluoride powderis amenable to atmospheric plasma spraying. An article having a sprayedcoating of the rare earth element oxyfluoride has higher resistanceagainst plasma etching than those articles having sprayed coatings ofrare earth element oxide and fluoride when used in a halogen gas plasma.High corrosion resistance ensures a long lifetime.

DESCRIPTION OF EMBODIMENTS

One embodiment of the invention is a thermal spray material comprisingrare earth element oxyfluoride particles having an aspect ratio of up to2 as shape index, an average particle size of 10 μm to 100 μm, and abulk density of 0.8 g/cm³ to 2 g/cm³, and containing not more than 0.5%by weight of carbon and 3% to 15% by weight of oxygen. This thermalspray material is effective for plasma spraying a rare earth elementoxyfluoride in air. In general, the thermal spray powder shoulddesirably meet the requirements including (1) smooth flow and (2) thatthe material is not decomposed into oxides by plasma spraying. The spraymaterial defined herein has these advantages.

The thermal spray material should preferably comprise particles ofspherical shape. When a spray material is fed into a flame for thermalspraying, a poor fluidity may make the material inconvenient to feedsuch as by clogging a feed tube. To ensure smooth flow, the spraymaterial should preferably consist of spherical particles. The particleshave an aspect ratio of up to 2, preferably up to 1.5. The “aspectratio” is used herein as one shape index of the three dimensions andrefers to a ratio of length to breadth of a particle.

The rare earth element used in the rare earth element oxyfluoride spraymaterial may be selected from among yttrium (Y) and Group 3A elementsinclusive of lanthanum (La) to lutetium (Lu). Of these, yttrium (Y),gadolinium (Gd) and erbium (Er) are preferred. A mixture of two or morerare earth elements is also acceptable. When such a mixture is used, thespray material may be obtained by agglomerating a mixture of rawmaterials, or by forming particles of a single element and mixing suchparticles of different elements prior to use.

The spray material has an average particle size of 10 μm to 100 μm,preferably 15 μm to 60 μm. As used herein, the average particle size isdetermined as a weight average value D₅₀ (i.e., a particle diameter ormedian diameter when the cumulative weight reaches 50%) by a particlesize distribution measurement unit based on the laser lightdiffractometry. If the particle size of spray material is too small,such particles may evaporate in the flame, resulting in a lower yield ofspraying. If the size of spray material is too large, such particles maynot be completely melted in the flame, resulting in a sprayed coating ofdeteriorated quality.

Particles as agglomerated to constitute the spray material should besolid, i.e., filled to the interior (or free of voids), because solidparticles are stable (or do not chip or collapse) during handling, andbecause the problem arising from voids in particles that undesirable gascomponent can be trapped in voids is avoidable. In this respect, thespray material should have a bulk density of 0.8 g/cm³ to 2 g/cm³,preferably 1.2 g/cm³ to 1.8 g/cm³.

The atmospheric plasma spraying of rare earth element oxyfluoride has apossibility that the oxyfluoride is decomposed into oxide. Particularlywhen the spray material (or powder) contains a noticeable amount ofwater or hydroxyl, it facilitates decomposition of the oxyfluoride intoa rare earth element oxide and the liberated fluorine forms a gas suchas hydrogen fluoride. The resulting sprayed coating becomes a mixture ofrare earth element oxide and rare earth element fluoride. In thisregard, the raw material to be agglomerated into the spray powder shouldpreferably have a water or hydroxyl content of up to 10,000 ppm, morepreferably up to 5,000 ppm, and even more preferably up to 1,000 ppm.

The spray material (or powder) contains carbon in a concentration of notmore than 0.5% by weight, preferably not more than 0.3% by weight, andmore preferably not more than 0.1% by weight. If the carbon content istoo high, such carbon can react with oxygen of the rare earth elementoxyfluoride to form carbon dioxide, causing decomposition of the rareearth element oxyfluoride. As long as the carbon content is limited low,decomposition of the rare earth element oxyfluoride during thermalspraying is inhibited and a satisfactory coating of rare earth elementoxyfluoride is deposited.

The rare earth element oxyfluoride spray material defined above can beprepared by agglomerating (or granulating) rare earth elementoxyfluoride or by mixing rare earth element oxide and rare earth elementfluoride and agglomerating the mixture. For example, the spray materialis prepared by dispersing a starting powder in a solvent such as wateror an alcohol of 1 to 4 carbon atoms to form a slurry having aconcentration of 10 to 40% by weight and agglomerating the slurry byspray drying or analogous technique. When rare earth element oxide andrare earth element fluoride are mixed, the mixture may consist of 10 to70% by weight of rare earth element oxide and the balance of rare earthelement fluoride.

Alternatively, the spray material may be prepared by mixing a rare earthelement oxyfluoride with an organic polymer serving as a binder such ascarboxymethyl cellulose and deionized water to form a slurry andagglomerating by spray drying or analogous technique. Examples of thebinder used herein include polyvinyl alcohol and polyvinyl pyrrolidoneas well as carboxymethyl cellulose. The binder is typically added in anamount of 0.05 to 10% by weight based on the weight of the rare earthelement oxyfluoride to form a slurry.

The particles as agglomerated are fired at a temperature of 600° C. to1600° C. in air, vacuum or an inert gas atmosphere for the purpose ofremoving the binder and water. Firing in an oxygen-containing atmosphereis preferred for carbon removal.

By plasma spraying the resulting spray material to a substrate, a rareearth element oxyfluoride-sprayed article is obtainable. The sprayedcoating on the substrate should have a carbon content of not more than0.1% by weight, preferably 0.01 to 0.03% by weight and an oxygen contentof 3 to 15% by weight, preferably 5 to 13% by weight.

Thermal spraying to a component of the semiconductor fabricationequipment is desirably atmospheric plasma spraying or vacuum plasmaspraying. The plasma gas used herein may be nitrogen/hydrogen,argon/hydrogen, argon/helium, argon/nitrogen, argon alone, or nitrogengas alone, but not limited thereto. Examples of the substrate subject tothermal spraying include, but are not limited to, substrates ofaluminum, nickel, chromium, zinc, and alloys thereof, alumina, aluminumnitride, silicon nitride, silicon carbide, and quartz glass whichconstitute components of the semiconductor equipment. The sprayedcoating typically has a thickness of 50 to 500 μm. The conditions underwhich the rare earth element oxyfluoride powder is thermally sprayed arenot particularly limited. The thermal spraying conditions may bedetermined as appropriate depending on the identity of substrate, aparticular composition of the rare earth element oxyfluoride spraymaterial, and a particular application of the resulting sprayed article.

The resulting sprayed article has higher resistance against plasmaetching (i.e., corrosion resistance) than sprayed coatings of rare earthelement oxide and fluoride. Thus a long lifetime is available.

EXAMPLE

Examples are given below by way of illustration and not by way oflimitation.

Examples 1 to 4 and Comparative Examples 1 and 2 Preparation of SprayPowder

A spray powder material was obtained by providing a starting powder ormixing ingredients in a predetermined ratio to form a starting powder asshown in Table 1, dispersing the starting powder in a binder (Table 1)to form a slurry, agglomerating in a spray dryer, and firing underselected conditions (Table 1). The resulting spray powder was measuredfor particle aspect ratio, particle size distribution, bulk density, andoxygen, fluorine and carbon concentrations. The results are shown inTable 1. Notably, the particle size distribution was measured by thelaser diffraction method, the fluorine concentration analyzed bydissolution ion chromatography, and the carbon and oxygen concentrationsanalyzed by the combustion and infrared (IR) spectroscopy method. Theaspect ratio of particles was determined by taking a scanning electronmicroscope (SEM) photo, measuring the length and breadth of 180particles in the photo, and averaging.

Preparation of Sprayed Article

The spray powder materials in Examples 1 to 4 and Comparative Examples 1and 2 were air plasma sprayed to aluminum substrates using a gas mixtureof 40 L/min of argon and 5 L/min of hydrogen. The resulting articles hada sprayed coating of about 200 μm thick. The sprayed coatings of powdermaterials in Examples 1 to 4 looked black, whereas the sprayed coatingsof powder materials in Comparative Examples 1 and 2 were white. Thecarbon and oxygen concentrations of each sprayed coating were measuredby the combustion and IR method. The results are shown in Table 1.

Corrosion Resistance Test

Each article was masked with masking tape to define a masked and exposedsection before it was mounted on a reactive ion plasma tester. A plasmacorrosion test was performed under conditions: frequency 13.56 MHz,plasma power 1,000 watts, gas mixture CF₄+O₂ (20 vol %), flow rate 50sccm, gas pressure 50 mTorr, and time 12 hours. At the end of the test,a step formed between the exposed and masked sections due to corrosion.The height of the step was measured at 4 points by a laser microscopeand averaged as an index for corrosion resistance. The results are shownin Table 1.

TABLE 1 Example Comparative Example 1 2 3 4 1 2 Start powder, particlesize Y₂O₃ 15 YOF 100 Gd₂O₃ 30 Er₂O₃ 40 Y₂O₃ YF₃ 100 D₅₀ 0.3 μm wt % 2.0wt % 1.1 μm wt % 0.3 μm wt % 1.0 100 2.0 wt % YF₃ 85 μm GdF₃ 70 ErF₃ 60μm wt % μm 1.8 μm wt % 1.5 μm wt % 2.5 μm wt % Agglomeration Start 30 wt% 20 wt % 25 wt % 35 wt % 35 wt % 25 wt % powder Binder* CMC 12 CMC 8PVP 8 PVP 5 CMC 10 CMC 5 wt % wt % wt % wt % wt % wt % Firing AtmosphereAir N₂ Air Vacuum Air Air Temperature 800° C. 900° C. 900° C. 900° C.1500° C. 800° C. Time 4 h 3 h 3 h 6 h 15 h 20 h Analysis of Aspect ratio1.2 1.5 1.3 1.3 1.5 1.5 spray powder D₁₀ 26 μm 18 μm 25 μm 30 μm 17 μm35 μm D₅₀ 46 μm 28 μm 48 μm 50 μm 30 μm 57 μm D₉₀ 68 μm 48 μm 75 μm 80μm 46 μm 80 μm Bulk density 1.4 g/cm³ 1.3 g/cm³ 1.6 g/cm³ 1.8 g/cm³ 1.6g/cm³ 1.5 g/cm³ Oxygen 4 wt % 13 wt % 4 wt % 5 wt % 21.3 wt % 0.5 wt %Fluorine 31 wt % 16 wt % 2.3 wt % 20 wt % 0 wt % 38 wt % Carbon 0.01 wt% 0.01 wt % 0.01 wt % 0.01 wt % 0.01 wt % 0.01 wt % Analysis of Oxygen 6wt % 13 wt % 6 wt % 8 wt % 21 wt % 2 wt % sprayed coating Carbon 0.02 wt% 0.01 wt % 0.02 wt % 0.02 wt % 0.05 wt % 0.11 wt % Corrosionresistance, step 3.6 μm 3.7 μm 3.8 μm 4.2 μm 4.7 μm 5.1 μm*Carboxymethyl cellulose, polyvinyl alcohol, and polyvinyl pyrrolidoneare abbreviated as CMC, PVA, and PVP, respectively.

As is evident from Table 1, the sprayed coatings obtained from the rareearth element oxyfluoride powder materials in Examples 1 to 4 havehigher resistance against plasma etching (corrosion resistance) than thesprayed coatings from the rare earth element oxide and fluoride inComparative Examples 1 and 2.

Japanese Patent Application No. 2012-183302 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A spray material comprising rare earth element oxyfluoride particleshaving an aspect ratio of up to 2, an average particle size of 10 to 100μm, and a bulk density of 0.8 to 2 g/cm³, and containing not more than0.5% by weight of carbon and 3 to 15% by weight of oxygen.
 2. The spraymaterial of claim 1 wherein the rare earth element is one or moreelements selected from the group consisting of Y and Group 3A elementsfrom La to Lu.
 3. The spray material of claim 2 wherein the rare earthelement is selected from the group consisting of Y, Gd and Er.
 4. Thespray material of claim 1 which is obtained by mixing 10 to 70% byweight of rare earth element oxide having an average particle size of0.01 to 5 μm and the balance of rare earth element fluoride having anaverage particle size of 0.1 to 5 μm, agglomerating, and firing.
 5. Arare earth element oxyfluoride-sprayed article comprising a substrateand a sprayed coating which is deposited on the substrate by plasmaspraying the spray material of any one of claims 1 to 4, the sprayedcoating having a carbon content of not more than 0.1% by weight and anoxygen content of 3 to 15% by weight.